CHARACTERIZATION OF OTOLITHS OF COD AT FLEMISH CAP

Image Processing

Age estimation of a fish population and observation of its evolution over the years becomes a more and more important task for todays fishery. One method applied by almost all laboratories is based on the analysis of the otolith, a small bone like structure located in the ear canals of the heads of bony fish. The otolith grows during the lifetime of the fish producing ring like structures. Usually, the rings can be grouped to form yearly growth rings, or annuli, much like trees do: concentric rings around year 1 at the center. Although even daily growth can be seen. The age of the fish at the time of collection can be determined by counting the annuli, commonly called: reading the otolith.

We developed an approach - where many steps are already implemented as fully automatic - that is able to estimate the number of yearly growth rings for cod quite accurately. Our idea is as follows: we select an angular section of the otolith, this section is transformed into a rectangular area, where standard image processing techniques are used to extract the data of interest. In several phases of the proposed algorithm filtering is employed to deal with noise, checks (false rings) and high frequency components of the ring structures.